1. Technical Field
The instant disclosure relates to an encoder, and in particular, to a scanning light-guiding encoder by forward focusing.
2. Description of Related Art
The monitors in the existing art use mice to move the location of the data intended for processing. A mouse generally includes two sets of X and Y axes encoders for outputting sequential logic signals (such as 11, 10, 00, 01). The sequential logic signals are generated by abutting the mouse against the table surface or other surfaces and moving the mouse toward specific directions, thereby moving a data location of the monitor to a different location. The principle of the use of a mouse is to generate a movement of a point on a plane by the operation of the X and Y axis encoder. In other words, the operation of only one of the X axis encoder and the Y axis encoder only allows the movement of a point on a line. The encoder generally includes a light-emitting module (such as a light-emitting diode), a grating wheel (including blades) and an optical sensing module. The grating wheel has a structure similar to a mechanical gear which, when rotating, either shields the light generated by the light-emitting module or allows the light to pass through. When the light is shielded by the grating wheel, the optical sensing module generates an OFF (0) signal; and when the light passes through the grating wheel and is received by the optical sensing module, the optical sensing module generates an ON (1) signal. The OFF (0) and ON (1) signals are sequentially generated and form a sequential signal. For example, when the grating wheel rotates clockwisely, the sequential signal generated by the optical sensing module can be a continuous and repeated signal including 11, 10, 00, 01, 11, 10, 00, 01 . . . , and when the grating wheel rotates counter-clockwisely, the signals generated can be 01, 00, 10, 11, 01, 00, 10, 11, 10 . . . . These signals can be used in circuit cording.
Generally, the resolution (CPR, count per round) of the encoder increases when the number of the blades increases and the distance between two sensors decreases. However, when the included angle between two blades decreases, i.e., when the number of the blades increases, the outer diameter of the grating wheel increases. If the outer diameter of the grating wheel is fixed, when the number of the blades increases, the width of each of the blades decreases. However, due to the diffraction of the light, the extent that the width of the blades can be decreased is also limited. Specifically, when the light passing the blades diffracts and is not shielded by the blades, the signals generated by the two sensors of the optical sensing module will invariably be ON (1) signals, regardless of the rotating direction of the grating wheel. Therefore, the mouse is unable to generate different sequential signals according to the movement thereof.
FIG. 1A is the schematic view of the arrangement of a light-guiding encoder of the existing art. FIG. 1B shows a partial view of the blades of the light-guiding grating wheel 1a and the optical sensing module 3a of the light-guiding encoder of the existing art. The light-guiding encoder of the existing art includes the light-guiding grating 1a, a light-emitting module 2a and the optical sensing module 3a. In order to overcome the problem related to the diffraction of light, the encoder employs a light-guiding grating wheel 1a having a plurality of spherical surfaces S arranged continuously as a light-emitting surface for focusing the light emitted by the light-emitting module 3a. As shown in FIG. 1B, the optical sensing module 3a includes the optical sensing chips S1, S2 arranged on the same vertical axis. The light emitted from the light-guiding grating wheel 1a is focused at the optical sensing chips S1, S2 of the optical sensing module 3a. Specifically, the light-guiding grating wheel 1a of the light-guiding encoder in the existing art can generate the signals of [1, 1], [0, 1], [1,0] and [0,0] upon rotating to the first position (1), the second position (2), the third position (3) and the fourth position (4) respectively. However, as shown in FIG. 1B, the light-guiding grating wheel 1a in the existing art has to employ two blades for generating a set of coding sequence including four signals.
In sum, since the width of the light beam decreases after passing the spherical surfaces due to the focusing principle, the distance between the optical sensing module 3a and the light-guiding grating wheel 1a needs to be controlled to ensure that the light is received by the optical sensing module 3a, thereby generating the signal. In addition, in the existing art, the optical sensing chips S1, S2 of the optical sensing module 3a are arranged along a same vertical axis, and hence, the light-guiding grating wheel 1a employs two blades to complete a coding sequence [1,1], [0, 1], [1, 0] and [0, 0]. Therefore, the resolution of the light-guiding encoder cannot be significantly improved.
Therefore, there is a need in the art for improving the resolution of the light-guiding encoder while not increasing the dimension of the grating wheel and the number of the blades.